Abstract：
Cardiac fibrosis refers to the abnormal accumulation of extracellular matrix within the cardiac muscle, leading to increased stiffness and impaired heart function. From a rheological standpoint, knowledge about myocardial behavior is still lacking, partially due to a lack of appropriate techniques to investigate the rheology of in vitro cardiac tissue models. 3D multicellular cardiac spheroids are powerful and versatile platforms for modeling healthy and fibrotic cardiac tissue in vitro and studying how their mechanical properties are modulated. In this study, cardiac spheroids were created by co-culturing neonatal rat ventricular cardiomyocytes and fibroblasts in definite ratios using the hanging-drop method. The rheological characterization of such models was performed by Atomic Force Microscopy-based stress-relaxation measurements on the whole spheroid. After strain application, a viscoelastic bi-exponential relaxation was observed, characterized by a fast relaxation time (τ1) followed by a slower one (τ2). In particular, spheroids with higher fibroblasts density showed reduction for both relaxation times comparing to control, with a more pronounced decrement of τ1 with respect to τ2. Such response was found compatible with the increased production of extracellular matrix within these spheroids, which recapitulates the main feature of the fibrosis pathophysiology. These results demonstrate how the rheological characteristics of cardiac tissue vary as a function of cellular composition and extracellular matrix, confirming the suitability of such system as an in vitro preclinical model of cardiac fibrosis.
摘要：
心脏纤维化是指细胞外基质在心肌内的异常积累，导致僵硬增加和心脏功能受损。从流变学的角度来看，关于心肌行为的知识仍然缺乏，部分原因是缺乏适当的技术来研究体外心脏组织模型的流变学。3D多细胞心脏球体是强大而通用的平台，用于在体外对健康和纤维化的心脏组织进行建模，并研究其机械性能如何被调节。在这项研究中,通过使用悬滴法将新生大鼠心室心肌细胞和成纤维细胞以一定比例共培养来创建心脏球体。通过基于原子力显微镜的应力松弛测量对整个球体进行了此类模型的流变表征。施加应变后,观察到粘弹性双指数松弛，其特征在于快速弛豫时间(τ1)，然后是较慢的弛豫时间(τ2)。特别是,与对照相比，成纤维细胞密度较高的球体在两个弛豫时间上均显示减少，τ1相对于τ2的衰减更明显。发现这种反应与这些球状体内细胞外基质的产生增加是相容的，概括了纤维化病理生理学的主要特征。这些结果证明了心脏组织的流变特性如何作为细胞组成和细胞外基质的函数而变化。确认该系统作为心脏纤维化的体外临床前模型的适用性。
